Optoelectronic semiconductor components such as light-emitting diodes (LEDs), edge emitting lasers, vertically emitting lasers (VCSELs), laser arrays, photodiodes, solar cells, phototransistors and the like, are increasingly being used as key components in lighting technology, projection, data storage, printing technology, energy production and many other applications.
On the basis of the material systems AlInGaN, InGaAlP and AlGaAs, the entire spectral range from the ultraviolet through to the infrared can be covered for emitting or detecting semiconductor components. Particularly light sources based on the semiconductor systems mentioned have advantages with regard to their compactness and long lifetime compared to competing solution approaches such as, for instance, incandescent lamps or halogen light sources.
Innovative technological developments such as, for example, the integration of LED or laser projection units in a mobile telephone or into the backlighting of projection screens in this case require ever more compact and, in particular, flatter designs which, in addition, are intended to be producible in a cost-effective manner. In this case, present-day technologies are encountering their limits since the ultracompact, long-life semiconductor light sources or receivers which at the same time can be produced in a cost-effective manner, as demanded by the market, cannot be adequately realized using present-day conventional technologies.
Semiconductor components operated without protection under atmospheric conditions tend towards increased failure rates. Thus, investigations have been able to demonstrate that oxygen and/or moisture on semiconductor surfaces lead(s) to degradation of the corresponding components.
As described in M. Okayasu et al., “Facet oxidation of InGaAs/GaAs strained quantum-well lasers”, J. Appl. Phys., vol. 69, p. 8346 (1991), for example, in edge emitting GaAs lasers, the light-induced oxidation of the laser facet leads to absorption losses and, hence, to thermal heating which can ultimately lead to the thermal destruction of the laser facet (“catastrophic optical damage”) and thus to component failure.
In AlInGaN lasers having an emission range near a wavelength of 400 nm, intensified degradation of the components has been observed during operation in moisture, as described in V. Kümmler et al., “Gradual facet degradation of (Al, In)GaN quantum well lasers,” Appl. Phys. Lett., vol. 84(16), p. 2989 (2004) and T. Schödl et al., “Facet degradation of (Al, In)GaN heterostructure laser diodes,” Phys. Stat. Sol. (a), vol. 201(12), p. 2635-2638 (2004).
Investigations by atomic force microscopy, as described in T. M. Smeeton et al., “Atomic force microscopy of cleaved facets in III-V-Nitride Laser Diodes grown on free-standing GaN substrates,” Appl. Phys. Lett., vol. 88, 041910 (2006), demonstrated, at degraded laser facets of the group III nitrides, formation of oxide layers, the thickness of which is dependent on the respective composition of the underlying semiconductor layer.
To reduce the disturbing environmental influences in the case of LEDs of the material systems AlGaAs, InGaAlP and AlInGaN, the latter are generally adhesively bonded by conductive adhesives on leadframes and potted with a silicone or epoxy resin, but various problems can lead to failures. Thus, there is the risk, for example, of leakage current paths arising at chip or mesa edges, in particular in the region of the pn junction, which leakage current paths can lead to ageing effects or failures as a result of electrostatic discharges, that is to say so-called ESD failures (ESD: “electrostatic discharge”). Damage of this type can be brought about, for example, by migration of metal particles from the conductive adhesive.
To combat this problem in LEDs, the critical side areas of the active zone are often etched using so-called “mesa” technology and protected by dielectric passivation layers. Coating methods such as vapor deposition, sputtering or chemical vapor deposition (CVD) are used in that case.
However, layers deposited by the above methods that are usually used have the disadvantage, for example, that uniformly fashioning a formation over steep and in part irregularly shaped flanks from all sides is thereby possible only to an inadequate extent. In addition, the deposited layers often have microcavities on account of incorporated residual gases, impurities or incorporated voids. Owing to these porous structures of passivation or mirror layers, oxygen and moisture, for example, can reach the critical semiconductor surface and lead to component failures described above.
In semiconductor lasers of the conventional material systems AlGaAs, InGaAlP and AlInGaN, antireflection layers, passivation layers or dielectric highly reflective layers are generally applied to the sensitive laser facets. This coating is generally effected by vapor deposition, sputtering or chemical vapor deposition of the coating materials as described for instance in T. Mukai et al., “Current status and future prospects of GaN-based LEDs and LDs,” Phys. Stat. Sol (a), vol. 201(12), p. 2712-2716 (2004) and S. Ito et al., “AlGaInN violet laser diodes grown on GaN substrates with low aspect ratio,” Phys. Stat. Sol. (a), vol. 200(1), p 131-134 (2003).
To avoid failures owing to moisture or oxygen in laser diodes, AlInGaN laser diodes, for example, are packaged in hermetically impermeable TO-based housings such as, for instance, the housing types T038, T056 and T090, under inert gas. What is disadvantageous about that method is, first, the high mounting outlay associated with additional costs and, second, the risk that damage and, hence, failure of the laser diode cannot be prevented owing to permeabilities of the housing and/or residual moisture in the housing.
Such a cost-intensive and often inadequate measure for packaging laser diodes in a hermetically impermeable housing to thus increase component stability has the additional considerable disadvantage that this is associated with limited compactness with regard to design size and low flexibility with regard to integration of other optical components.
It could therefore be helpful to provide an optoelectronic component in which disadvantages mentioned above can be avoided to provide a method of producing an optoelectronic component.